Embodiments of the present invention relate to the generation of a pattern on a substrate using electron beams.
A conventional electron beam pattern generator typically comprises an electron beam column in which a single electron beam is generated, modulated, and directed onto a substrate to expose an electron-sensitive resist material on the substrate. A substrate support is used to support and move the substrate. An electron beam source generates the electron beam. A beam modulator modulates the intensity of the electron beam. Beam optics are used to focus the electron beam. A beam scanner is used to scan the electron beam across the substrate.
One problem with conventional pattern generators is that these systems typically use a single beam and, consequently, generate a pattern at relatively slow speeds because pixels are sequential exposed on the substrate in series. The exposure rate of single beam systems is further limited by the total beam current. As the total beam current is increased, electron to electron interactions cause excessive proximity errors by undesirably exposing regions of the substrate that neighbor target regions.
Multiple electron beam pattern generators use a plurality of electron beams to generate an electron beam pattern on a substrate and, consequently, can generally operate with better resolution and at higher speeds than single electron beam pattern generators. The multiple electron beams are accelerated to a high velocity at which they can be drawn from the electron source as separate and well-defined beams. However, the multiplicity and close spacing of the individual electron beams also result in distortions of the electron beams that limit the quality of the pattern formed on the substrate. For example, as the electron beams propagate towards the substrate, space charge interactions occur between the electrons in neighboring electron beams, blurring and distorting the cross-sectional shape of the electron beams. As the total beam current is increased, electron to electron interactions limit beam resolution, and hence upper limits are placed on beam current and exposure rate to ensure adequate optical resolution and critical dimension control.
Also, as the electron beams impinge on the substrate, the degree of exposure of a region on the substrate by one electron beam is undesirably affected by neighboring electron beams that simultaneously impinge on the substrate. Undesirable exposure can result from electrons from individual beams scattering upon impact and also due to localized heating of the substrate from the energy of multiple beams. In addition, cross-over regions where the multiple electron beams cross-over one another, such as during focusing of the beams, can result in beam to beam interactions that further reduce the resolution of the beams and increase beam error functions.
It is desirable to generate a pattern on a substrate using multiple electron beams having reduced beam interactions. It is further desirable to have a system capable of generating a pattern with multiple electron beams that exhibits reduced scattering or localized heating effects. It is also desirable to have a multiple electron beam pattern generating system capable of providing high exposure rate with good resolution.